1. Field of the Invention:
This invention relates to a rigid plastic container for food products and a method of making the container, with particular reference to a container having a body thermoformed from a sheet comprising a plurality of discreet layers which are held together in a contiguous structure without being securely bonded together, and therefore are insufficient to provide mutual reinforcement, said layers of the container body functionally secured in place after filling by an interlocking closure.
2. Description of the Prior Art:
In general, the packaging of many food products require a container having a high degree of protection from gas and/or water vapor permeation into or out of the container. For example, the packaging of a food product containing a high percentage of oils requires a container which is a good barrier to oxygen penetration since the oxygen will combine with oils to cause an off taste and rancidity. Other food products such as those high in starch and sugar content require a container which will prevent the pick up of water during storage. Containers having excellent gas and/or water vapor barrier characteristics are useful for the packaging of dry food stuffs which must be kept low in water content as, for example, dry soups, gravy mixes, and powdered sugar, or foods that require that a water content be maintained such as condensed soups, canned fruits and vegetables, or foods which must be kept free from oxygen such as meat products or other like foods containing oils and fats.
Since the price of metal cans over the past few years has continued to increase while the price of many plastic materials has decreased, there is an increasing demand by the food packaging industry for a relatively inexpensive plastic container which will provide excellent oxygen and water vapor barrier properties and will permit heat sterilization of canned foods without container failure. Although many rigid plastic food containers are known and are being used, the development of containers having excellent oxygen and water vapor barrier properties which will survive retort temperatures is a relatively recent development.
Containers exhibiting excellent gas and water vapor properties preferably have bodies comprising multilayered thermoplastic side and bottom walls. Typical illustrations of such containers are described in an application Ser. No. 12,036, filed on Feb. 17, 1970 and entitled "Packaging of Food Products" by Laddie M. Thomka and assigned to same assignee as the present invention. This application discloses the practical concept of a container having a body comprising a plurality of thermoplastic layers which will provide excellent gas and/or water vapor barrier properties and will withstand retort temperatures. In the specific embodiment of this application the layers forming the container body are secured together with adhesive layers and therefore provide mutual layer reinforcement for the container. As a result, a problem occurs during the container body thermoforming process in that the considerable scrap generated cannot be or is difficult to recycle, particularly since the various layers normally have incompatible thermoplastic resin compositions.